Groundwater Management Plan

For years the City of Tracy (City) relied upon its entitlement from the Delta-Mendota Canal and the underlying aquifer as its two main sources of water.

The City derived about 60 percent of its water supply from surface water, with the remaining 40 percent coming from groundwater. During periods of low demand, the City has been unable to use all of the Delta-Mendota entitlement within the basin. The City of Tracy wanted to develop a groundwater management plan, a groundwater monitoring plan, and the means to recharge the surplus surface water within the basin for future use.

The City selected GEI Consultants to assist in developing a groundwater management plan, performing hydrogeologic investigations of the area, developing a groundwater monitoring plan, evaluating methods for recharging the Delta-Mendota water, establishing a monitoring network for water quality and quantity, analyzing available aquifer storage, and developing a management plan for effectively managing the City’s water resources.

GEI assisted the City in preparation of CEQA documentation to allow the City to increase its use of groundwater supplies from 5,600 acre-feet to 9,000 acre-feet per year. No substantial evidence was found that the proposed extraction would have a significant effect on the environment. The results of the potential impacts and mitigating measures were documented in a mitigated negative declaration.

GEI designed and provided construction oversight of 18 clustered groundwater monitoring wells throughout Tracy to monitor groundwater levels and water quality. GEI has been evaluating the groundwater level, water quality, and subsidence since 2001, using a network of benchmarks established by the City.